Bore hole for hammer drive mechanism

ABSTRACT

A hammer piston reciprocates in a housing and impacts against an anvil in the housing which is integral with a drill bit, a drilling string rotating the housing during the repeated impacting of the piston against the anvil. Torque is transmitted from the housing through a plurality of segments to the anvil during the impacting action, transmission of the torque occurring from the segments through generally chordal surfaces formed on the anvil. Such generally chordal surfaces are preferably concave, but can be straight or planar. Alternatively, the torque can be transmitted directly from a housing member to the anvil through coengaging planar chordal surfaces on the housing member and anvil.

United States Patent 1191 Curington et al.

1111 3,804,181 Apr. 16, 1974 BORE HOLE FOR HAMMER DRIVE 1,078,953 11/1913 Prellyvitz 173/133 x MECHANISM 2,343,839 3/l944 Austin 287/53 SS [75] Inventors: Alfred R. Curln gton, Houston, Tex.; FOREIGN PATENTS OR APPLICATIONS Arlcher n J 524,676 5/1956 Belgium 287/53 ss Fu lerton, alif.

[73] Assignee: Baker Oil Tools, Inc., City of Primary Examiner-Henry C. Sutherland Commerce, Los Angeles County, Attorney, Agent, or Firm--Bernard Kriegel Calif. 22 Filed: Mar. 29, 1972 57 ABSTRACT [21] Appl. No.: 239,047 A hammer piston reciprocates in a housing and impacts against an anvil in the housing which is integral with a drill bit, .a drilling string rotating the housing [52] 5 2 during the repeated impacting of the piston against the 5 l I t 5 U02 anvil. Torque is transmitted from the housing through d l73/l 133 a plurality of segments to the anvil during the impact- 1 2 53 LK 3 ing action, transmission of the torque occurring from 64/9 the segments through generally chordal surfaces formed on the anvil. Such generally chordal surfaces are preferably concave, but can be straight or planar. [56] References Cited Alternatively, the torque can be transmitted directly UNITED STATES PATENTS from a housing member to the anvil through coengag- 3,311,117 3/1967 Collier et al. 173/66 X ing planar chordal surfaces on the housing member 3,595,323 7/l97l Schindler 173/80 and anviL 1,375,443 4/1921 Bayles l73/13l 2,608,180 8/1952 Curtis 173/132 14 Claims, 15 Drawing Figures 42 0 %E I \l ;45 5 I l 5 J4- 343 A 44 2 k .10 11 1 y/Q", 1 flj2 A cg a-w x s 1 i ear/:55 R 1 1; 4 g C .?9 ar 5 e 56 3 207 4 1 Q 4 511 [v g 1 L i9?16} 1 g 7 17 g g, 320. Q 4 i? m4 is PATENTED APR 16 I974.

SHEET 3 OF 5 BORE HOLE FOR HAMMER DRIVE MECHANISM The present invention relates to drill bit apparatus for drilling a bore hole in a formation, and more particularly to pneumatically operated apparatus that imparts a percussive action to an anvil and drill bit integral therewith while the latter are preferably rotated.

During the impacting action of an air hammer piston against the anvil portion of a drill bit, the anvil and drill bit are rotated by rotating the housing of the apparatus, so that the face of the drill bit covers substantiallythe full area of the bottom of the bore hole being drilled in a formation, torque being transmitted from the housing to the anvil through a key and keyway type of spline connection, in which a multiplicity of elongate keys and keyways are disposed circumferentially around the anvil and the housing member associated therewith. Such key and keyways spline interconnections for transmitting torque between the housing and the anvil effect a substantial reduction in the cross-sectional area of the anvil throughout the length of-the key and keyway portion, which results in loss of the'air hammer energy transmitted throughout the length of the anvil and bit. This is believed to be .due to the fact that the impacting of the hammer piston against the anvil creates longitudinal stress pulses which travel through the bit from the anvil end to the face end .of the bit. These stress pulses or stress waves remain constant in magnitude until such time as they encounter a change in cross-sectional area of the bit. At these changes in cross-sectional area; part of the pulse is reflected back and a smaller magnitude pulse continues in the original direction. The amount of energy reflected back and transmitted through an intersection depends upon the relative areas before and after the intersection. Therefore, it is desirable to have as few cross-sectional area changes as possible in the bit, and also the ratio of areas before and after the intersection should be as near. one as possible. The lossof energy in the reflected stress wave that is travelling back from the bit face to the anvil end only has a small effect .on the frequency at which the air hammer runs. This is because the energy that is reflected on the bit face and getsback through all the intersections of the bit is transmitted back into the piston when it reaches the anvil end, if the piston is still in contact with the bit anvil. Ideally, this energy should be zero because the initial stress wave that reaches the bit face under ideal conditions would be transmitted to the rock face and dissipated in breaking rock. However, in actual practice, this never happens; therefore, the design of bit has some small effect on the frequency at which the hammer operates.

In addition to the above loss of energy, the key and keyways splinetype of connection is relatively costly to manufacture,and are subject to excessive wear of the coengaging and readily slidable parts. The wear that does occur is uneven throughout the length of the key and keyway spline region.

By virtue of the present invention, a torque transmitting spline type of drive is provided between the housing and the anvil and bit, which has a lesser decrease in cross-sectional area throughout its length than in the prior bits, resulting in a substantial decrease in the amount of energy lost through the bit as a result of reflections created by the transmitting of the longitudinal stress pulses from the upper end of the anvil to the lower drilling face of the bit. In addition, the torque transmitting drive connection provided between the housing, usually a housingsub or member forming the lower end of the housing, and the anvil can be manufactured at a substantially reduced cost. Wear between the anvil and the torque transmitting parts engaging it is uniform, such that the drive connection between the housing and anvil has a much longer life than prior types of drive, such as the key and keyway .types heretofore used. Moreover, when wear does occur, the parts are readily replaceable, such parts requiring replacement being comparatively few in number and relatively inexpensive.

This invention possesses many other advantages and has other objects which may be made more clearly apparent from a consideration of several forms in which it may be embodied. Such forms are shown in the drawvings accompanying and forming part of "the present specification. These forms will now be described in detail for the purpose of illustrating the general principles of the invention; but it is to beunderstood that such detailed description is not to .be taken in a limiting sense.

Referring to the drawings:

FIGS. 1a and 1b together constitute a longitudinal section through an apparatus embodying the invention, with parts in their relative positions in which the hammer piston has completed delivering an impact blow against its companion anvil and the drill bit secured thereto, FIG. lb being a lower continuation of FIG. 1a;

FIGS. 2a and 2b are views similar to FIGS. la and lb, with the hammer piston at its upper position, FIG. 217 being a lower continuation of FIG. 2a,"

FIGS. 3a and 3b are views-similar to FIGS. la and lb, illustrating the relationship of the parts with the bit off the bottom of the hole, allowing air to be circulated through the apparatus, FIG. 3!) being a lower continuation ofFlG/3a;

FIG. 4 is a cross-section taken along the line 4-4 on FIG. 41);

FIG. 5 is a cross-section taken along the line 5-5 on FIG. lb; v

FIG. 6 is an exploded isometric projection of a portion of the drive mechanism between the housing an the anvil of the apparatus;

' FIG. 7 is a fragmentary longitudinal section through another embodiment of the lower portion of the apparatus; I

FIG. 8 is-a cross-section taken along the line 8-8 on FIG. 7;

FIG. 9 is a fragmentary longitudinal section of still another embodiment of the invention;

FIG. 10 is a cross section taken along the line l0l0 on FIG. 9;

FIG. 11 contains curves showing the greater crosssectional area maintained through the anvil bit illustrated in FIGS. 1 to 6, inclusive, as compared with a key and keyway spline type of drive connection;

tom of the hole. The apparatus includes an elongate housing structure consisting of a plurality of parts. A main central section 11 of the housing structure has its upper end threadedly secured to an upper head 12, which, in turn, is threadedly secured to a sub 13 having a boxl4 threadedly attached to the pin 15 at the lower end of an adjscent drill'pipe section B. The lower end of the intermediate housing section is threadedly attached to a lower head or drive sub 16 having rotatable torque transmitting spline type connection 17 with an anvil l8 integral with the impact drill bit C of any suitable form, against which impact blows will be directed while the drill pipe string B and apparatus A are being rotated, to insure that the cutting portions of the drill bit will cover the entire cross-sectional area of the hole bottom E.

The upper housing head 12has one or a plurality of inlet passages 19 opening through its upper end, their lower ends communicating with an annular inlet passage 20 between the outer housing section 1 1 and a cylinder sleeve 21 integral with and depending from the housing head. This cylinder sleeve has upper inlet ports 22 and lower inlet ports 23 communicating with the annular inlet passage andadapted to be placed in communication with the cylinder space 24 within the cylinder sleeve. Below the lower inlet ports 23, the cylinder sleeve 21 carries a suitable seal ring 25 for sealing against a wall 26 of the housing section 11, which is of smaller internal diameter than the wall 27 of the housing section portion surrounding the annular inlet pas sage 20.

A hammer piston 28 is reciprocable within the housing structure 10 and its cylinder sleeve 21, this piston being adapted to deliver an impact blow against the upper end 29 of the anvil l8 splined to the lower head 16 and extending upwardly into the lower portion 30 of the housing section 11, this lower portion and its inner I wall 26 having a substantially greater internal diameter S than the internal diameter T of the cylinder sleeve 21. In fact, the internal diameter S of the cylinder section is greater than that of the cylinder sleeve from the location of the cylinder sleeve seal ring 25 to the upper end of the lower head 16. An elongate circumferential internal groove 31 in the housing wall will function as an annular exhaust passage 32, as described hereinbelow.

The piston 28 has an enlarged outside diameter portion 33 reciprocable along the greater diameter wall 26 of the housing structure, the lower part 34 .of this piston portion having a reduced external diameter so as to clear a limit ring 35 fitting within an internal circumferential groove 36 in the housing section, and on which a downwardly facing piston shoulder 37 is adapted to rest when the drill bit has been removed. When the drill bit C is in engagement with the bottom of the bore hole, it is held thereagainst by the lower end 38 of the lower head bearing against an upwardly facing drill bit or anvil shoulder 39.

The hammer piston 28 has a longitudinal impact passage 42 opening through its upper end and having a lower lateral branch 43 communicating with the annular space or passage 44 between an upper, smaller diameter piston portion 45 and the enlarged diameter wall 26 of the housing section below the housing sleeve 21. The lower end of this annular passage 44 is adapted to communicate with the annular exhaust passage 32 which is in communication with a lateral exhaust port 46 extending from a central exhaust passage 47 in the lower portion of the piston to the periphery of the enlarged piston portion. This central passage 47 receives the upper portion of a sleeve 48 piloted within a central air exhaust passage 49 extending through the anvil, being secured to the anvil in any suitable manner, as by welding material 48a. The exhaust passage 49 extends downwardly through the anvil 18 and drill bit C, discharging from the latter against the bottom E of the hole to clean the latter and the drill bit of cuttings, conveying the cuttings upwardly around the housing 10 and the drill pipe B to the top of the bore hole.

The hammer piston or impacting member also has a longitudinal return passage 50 opening through its lower end, its upper portion communicating with a port 51 opening into an annular inlet groove 52 in the smaller diameter portion 45 of 'the piston adapted to communicate with the lower inlet ports 23 when the air hammer is in its lower position engaging the anvil, as disclosed in FIGS. 1a and lb. At this time, the upper inlet ports 22 are closed by the piston. Suitable piston rings 53, 53a, 53b, may be mounted on the piston for preventing leakage therealong. As disclosed, an upper piston ring 53 occupies aposition above the upper inlet ports 22 during the drilling operation, intermediate and lower piston rings 53a, 53b straddling the lower inlet ports 51 when the hammer piston 28 engages the anvil 18.

The smaller diameter piston portion 45 has a further reduced diameter portion 54 below the lower piston ring 53b, which defines an annular air inlet passage 56 with the cylinder sleeve 21, so that upon elevation of the piston in the housing structure and its cylinder sleeve, the annular inlet passage 56 will be placed in communication with the lower inlet ports 23 to permit compressed air to flow from the latter through the annular passage and into the lower end 43 of the impact passage 42, such compressed air then passing into the cylinder 24 above the piston 28 for the purpose of forcing the latter downwardly and strike an impact blow against anvil 18. During the earlyportion of upward movement of the piston, the upper end 57 of its enlarged piston portion engages the cylinder wall 26 above the annular exhaust groove 32 to shut off communication between the impact passage 42 and exhaust port 32. Additional upward movement of the piston will then place theannular inlet passage 56 in communication with the lower inlet ports 23 to feed compressed air into the impact passage 42, as described above.

As the'piston moves downwardly, the lower end 58 of the upper piston portion of smaller diameter will move across the lower inlet ports 23 to close-them from communication with the annular inlet passage 20, further downward movement then moving the shut-off corner 57 into the annular exhaust passage 32, allowing the compressed air above the piston and in the impact passage 42 to exhaust through the exhaust port 46, cenv tral exhaust passage 47, inner sleeve 48, and exhaust air passage 49 to the bottom of the hole, the energy imparted to the piston 28 by the compressed air driving it downwardly to impact it against the anvil 18. Just before impact occurs, the annular inlet groove 52 is placed in communication with the lower inlet ports 23, compressed air flowing therethrough and through the return passage 50 to the lower end of the piston, such air acting on the piston to drive it back toward its upper position. A relatively short upward travel again places the piston portion 59 below the groove 52 across the lower inlet ports 23 to shut off communication between them and the return passage 50, the air below the piston expanding and driving the piston upwardly, once again compressing the air in the cylinder space 24 above the piston. As the return air drives the piston upwardly, its lower shoulder 37 will move above the lower end 70 of the exhaust groove 32, allowing the return air to exhaust from below the piston around the reduced diameter portion 34 into the exhaust groove 32, from where it flows through the passages 46, 47, 48 and 49 to the bottom of the bore hole D.

It will be noted that immediately before the piston 28 impacts against the anvil 18, the shut-off corner 57 moves off the cylinder wall 26 above the exhaust groove 32, permitting the compressed air that has driven the piston downwardly to exhaust through the passages 46, 47, 48, 49 into the bottom of the hole. Such exhaust action takes place after the piston shoulder 58 has moved below the lower inlet ports 23. Shortly before the piston impacts against the upper end of the anvil, the annular inlet groove 52 is placed in communication with the lower inlet ports 23, allowing the compressed air to flow through the return passage 50 in order to drive the piston 28 back upwardly. The shut-off corner 57 moves above the exhaust groove 31 shortly before the piston portion 59 below the annular inlet groove 52 moves across the lower inlet ports 23 to shut off air flow into the return passage 50, the air below the piston expanding and driving the hammer piston upwardly, compressing the air in the cylinder space 24 above the piston. Near the upper end of the piston stroke, the shoulder 58 moves above the lower inlet ports 23 to feed'compressed air through the impact passage 42 to the upper end of the piston, the compressed air driving the piston downwardly.

It will be noted that the compressed air that drives the piston downwardly acts over the full cross-sectional area S of the piston, which is the area of the-enlarged piston portion 33. This piston area can be made quite large since the enlarged piston portion slides along the inner wall 26 of the housing section. There are no restrictions in the housing that can reduce the piston diameter over which the compressed air acts, such asthe restriction in the housing imposed by the cylinder sleeve 21. Thus, the area S over which the compressed air is acting on the power stroke of the hammer piston is the sum of the cross-sectional area T of the smaller diameter piston plus the annular area U which is the annular area between the periphery of the smaller diameter piston portion and the periphery of the enlarged piston portion. The compressed air for returning the hammer piston acts across the annular area R between the periphery of the enlarged piston portion and the inner wall of the exhaust passage 47 in the lower portion of the piston. However, such area R need not be large, since the compressed air flowing through the return air passage need only return the piston to the upper end of its stroke, compressing the air in the cylinder space bit, insuring that the bottom of the bore hole will be swept free of cuttings, and insuring the maximum penetration of the cutting elements of the bit into the formatron.

With the bit C elevated from the bottom E of the bore hole, air can be circulated through it relatively freely. With'the bit off bottom (FIGS. 3a, 3b), it will drop downwardly of the housing structure, moving its anvil portion 18 downwardly until its downwardly facing shoulder 80 engages the upper end of drive segments or keys 81 mounted in the lower head or drive sub 16, as described in detail hereinbelow. The piston 28 moves downwardly to the extent limited by engagement of its lower end with the upper end of the anvil, the upper end 82 of the piston then being disposed below the upper inlet circulating ports 22. At this time, the shut-off corner 57 at the upper portion of the enlarged diameter of the piston is disposed well within the exhaust groove 31. Accordingly, compressed air can flow from the drill pipe B through the sub 13 and the inlet passages 19 into the annular inlet passage 20, proceeding through the inlet circulating ports 22 into the cylinder sleeve 21, and then passing through the impact passage 42, 43 to the exterior of the piston, flowing through the groove 31 and into the exhaust port 46, continuing to flow into the central exhaust piston passage 47, inner sleeve 48, and through the exhaust air passage 49 for discharge from the lower end of the bit.

ln FIGS. 1a and lb, the apparatus is illustrated with the bit C resting against the bottom E of the hole and the hammer piston 28 having just delivered its blow to the anvil 18. The air in the cylinder above the piston has exhausted through the impact passage 42 and the groove 31 into the exhaustport 46, continuing to exhaust through the passages 47, 48, 49 from the bit and against the bottom of the bore hole. The compressed air flows through the return passage 50 to the bottom of the hammer piston, acting in an upward direction over the annular area R of the piston to drive it upwardly. Initially, the shut-off corner 57 moves above the exhaust groove 31 to close it from the impact passage 42, whereupon the piston 59 below the annular groove shuts off the lower inlet ports 23, the expanding air below the piston continuing to drive upwardly and compressing the air that remains in the cylinder space 24 above the piston, providing an air cushion to prevent the piston from impacting against the cylinder head 12. The downwardly facing piston shoulder 58 has now moved above the lowermost ends of the lower inlet ports 23, permitting compressed air to flow from the 24 above the piston so that it will not impact against the cylinder head 12. However, the energy required to compress the air is recovered when the air later expands in driving the piston downwardly on its power stroke.

It is to be noted that all of the compressed air entering the apparatus exhaust through the lower end of the inlet ports 23 into .the annular inlet passage 56, and through the impact passage 43, 42 to the upper portion of the piston (FIGS. 2a and 2b), which then causes the compressed air to drive the piston 28 downwardly and deliver an impact blow against the anvil. near the limit of its downstroke, the shut-off corner 57 moves into the region of the exhaust groove 31, permitting the compressed air to exhaust through the bit, as described above, the return passage 50 again being placed in communication with the lower inlet ports 23, the piston impacting against the anvil, and the foregoing cycle of operation repeated.

The apparatus disclosed in the drawings also includes a water check valve device 200 F IG. 1a). As shown, the upper housing head 12 has a guide bore 201 opening through its upper end and receiving a valve stem 202 terminating in an upper valve head 203 adapted to engage a central valve seat 204 on the upper sub. The valve stem and its head are urged upwardly to place the head 203 in engagement with its companion set 204 by a helical compression spring 205 bearing against the lower end of the valve stem and against the base 206 of the guide bore. A bleeder passage 207 is provided in the upper housing head, its upper end communicating with the guide bore 201 and its lower end with a lateral bleeder port 208, to avoid trapping of fluid in the bore and itspotential interference with the movement of the valve head.

Compressed air pumped down through the drill pipe string B will shift the valve head 203 downwardly from engagement with its seat 204, enabling the compressed air to flow into an upper recess 209 in the upper head through which the inlet passages 19 open. Any tendency for water or other liquid to flow upwardly into the apparatus is precluded by the upward seating of the valve head 203 against its seat 204.

During the reciprocation of the piston 28 within the housing structure to deliver repeated impact blows against the anvil 18, the drill pipe string B and apparatus A are being rotated while suitable downweight is imposed on the drill pipe andhousing structure, the lower end 38 of the head or drive member continually bearing against the bit or anvil shoulder 39, holding it against the bottom E of the bore hole. Rotary motion is transmitted from the housing structure 10 through the spline-like connection to the anvil 18.As disclosed in FIGS. 1 to 6, this spline-like drive connection includes a plurality of circumferentially spaced segments or keys 81, each of which is disposed in an opening 300 extending through the upper portion of the drive member 16, the outer drive surfaces 301 of the keys engaging the inner wall 302 of the housing, while the inner surfaces 303 of the keys engage companion generally chordal surfaces 304 formed in the anvil 18. The outer curved wall 305 of each segment is concave in shape and forms a passage 306 with theopposed inner wall 302 of the housing. The inner .wall or surface 303 of each segment is convex in shape, conformingto the companion concave surface 304 in the anvil 18, this surface being elongate and of substantially greater length than the segment 81 and forming the base of the recess or' groove 307 cut or otherwise formed in the anvil.

The outer portions 308 of the convex segment surfaces engage companion surfaces 309 forming the sides of the opening through the drive member 16. The upper end 310 of each segment engages the upper side 311 of the opening in the drive member, while the lower end 312 of each segment engages the lower end 313 of the opening, there being upper and lower transverse grooves 314, 315 formed in each segment, to provide communication between the space 316 between the anvil and housing above the segment and the space 317 within the housing below the segment; that is, air can bleed from the space 316 above each segment through the upper groove 314 into the passage 306 between each segment and housing, continuing through the lower groove 315 into the lower portion of the anvil recess 317. Normally, during the imposition of drilling weight on the bit by virtue of the lower end of the head 16 engaging the bit shoulder 39, circumferential grooves 318 in the drive member 16 below its openings 300 provide a labyrinth seal engaging the cylindrical periphery 319 of the anvil below its recesses 304. However, when the drill bit is picked up off bottom E, with the anvil and bit dropping downwardly to the position illustrated in FIGS. 3a and 3b, the downward movement of the bit anvil being limited by engagement of its upper head with the upper ends of the segments 81, the cylindrical periphery 319 of the anvil 18 is disposed below the labyrinth seals 318, placing the recesses or grooves 304 in the anvil in communication with circumferentially spaced internal relief grooves 320 in the interior of the drive member 16 that opens through its lower end. Thus, upon elevating of the bit from the bottom of the hole E and its downward dropping, air will not be trapped between the lower end of the hammer piston 28 and the region between the upper portion of the anvil 18 and housing, which might tend to cause the piston to continue reciprocating in the housing 11, instead of the anvil and piston occupying the lower position illustrated in FIGS. 3a and 3b in which air can be caused to circulate through the apparatus, anvil 18 and bit C without effecting operation of the apparatus.

A large torque transmitting surface between the segments 81 and the anvil 18 is provided. Thus, the torque transmission occurs between one of the side walls 309 of the drive member 16, through the surface 308 to each of the segments or keys 81, and from the convex surface 303 of such segment to the concave surface 304 of the anvil engaged therewith. During the transmission of the torque for the purpose of rotating the drill bit C during the operation of the air hammer, the anvil and bit can move longitudinally with respect to the segments 81 and the housing 16, 11, but in view of the comparatively large area of the contacting surfaces between the segments 81 and the companion concave walls 304 of the anvil 18, wear between the parts'that does occur may be confined essentially to the segments, which are readily replaceable. Despite such large area of contact, the cross-sectional area of the anvil 18 and bit C throughout its length has been decreased to a substantially lesser extent than in torque transmitting arrangements embodying key and keyway spline types of connections. This is exemplified in the graph of FIG. 11, in which the cross-sectional area is plotted along the length of the anvil and bit, beginning at its upper face 29 and extending downwardly to the drilling face 400 of the bit. Curve M shows'the crosssectional area at each point along the length of the prior spline types of connections between the housing 16 and anvil that shows the cross-sectional area at each point along the length of the anvil and bit of a prior drive connection embodying the key and keyway splines. Curve B shows the cross-sectional area at each point along the length of the bit illustrated in FIGS. 1 to 6, from its upper end 29 to its lower end drilling face 400. It is evident that the cross-sectional area at Curve B is greater from the upper end 29 of the anvil to the bit shoulder 38 against which the lower end of the head or drive member 16 bears to transmit drilling weight therethrough. Thus, there is less change in crosssectional area throughout the length of the anvil and bit at Curve B then in Curve M, since the cross-sectional area at the bit shoulder 38 is the same in both Curve M and in Curve B, as indicated by the points 401.

The result of a less change in cross-sectional area occurring throughout the length of the anvil bit is a reduction in the loss due to reflections through the anvil and bit of Curve B. It can be shown that the loss due to reflections created by longitudinal stress pulses is approximately percent in the drive mechanism of Curve B; whereas, the loss through the prior drive mechanism, represented by Curve M, is about 17 percent. Thus, the loss of energy transfer through applicants bit, as represented by Curve B, results in about a 12 percent improvement over the bit represented by Curve M.

The drive mechanism illustrated in FIGS. 1 to 6 is more economical to manufacture than the prior key and keyway spline types of drives used in air hammers. Moreover, when wear does occur, it is relatively easy to replace the drive segments 81 without having to replace the entire drive member or sub 16, as in the prior air hammers. As noted above, because of the large torque transmitting surface between the segments 81 and the anvil 18, the wear in applicants drive mechanism may be confined to the segments, rather than to the anvil and'drive sub, as in prior drive mechanisms The drive mechanism illustrated in FIGS. 7 and 8 is similar to FIGS. 1 to 6, except that the drive segments 81a are of a different shape. Thus, the drive member 16 has openings 300a therein, such as circumferentially spaced openings, in which segments 81a are disposed, the exterior 81b of the segments being curved and conforming to the wall of the surrounding housing 30 while the inner surface 810 of each segment is a chordal surface bearing against a companion chordal surface 81d formed on the anvil, such flat and chordal surface 810 of each segment engaging companion surfaces 300a defining the sides of the opening in which the segment is disposed. The top 310a and bottom 312a of each segment conform closely to the top and bottom of the opening 300a in the drive member; whereas, the segment itself is disposed within an elongate recess or groove 600 formed in the anvil, to permit the anvil and bit to drop downwardly to the position shown in FIG. 3b, in which air can circulate freely through the apparatus for discharge from the lower 'end of the bit, while preventing any air from being trapped between the 4 anvil and housing (as in FIG. 3b, grooves 320).

The engagement between the inner surface 810 of each segment 81a and the companion surface 81d on the anvil is along a true chordal plane. A similar engagement is present between the curved segments 81 and the converse walls or surfaces 304 of the anvil 18, such as shown in FIG. 4. The essential structure and mode of operation and the advantageous results achieved are substantially the same in both the FIG. 4 and the FIG. 8 embodiments, the coengaging drive surfaces 303, 304 and 81c. 81d in both embodiments being referred to herein as generally chordal surfaces; that is, extending transversely across the anvil 18, as distinguished from a generally radialkey and keyway spline type of connection of the prior. art devices.

In FIGS. 9 and 10, the spline connection between the drive member portion 16 of the housing and anvil 1812 also includes chordal torque transmitting surfaces 81 f, 81g between the drive member and the anvil 18b. Thus, the anvil has a portion of extended length provided with one or more chordal or flat faces 81g on its periphery which engage companion chordal or flat faces 81f on the drive member. The anvil 18b is inserted upwardly into the drive member 16, and a split. expandable ring 605 is then disposed over the upper end of the anvil, the drive member 16 then being threaded fully upwardly into the housing 30, the split ring engaging a downwardly facing housing shoulder 606. This ring projects inwardly of the inner surface 81f of the drive member, so that the upper head on the anvil will limit downward movement of the anvil 18b and bit C within the housing when the bit is elevated from the bottom E of the bore hole.

During the operation of the air hammer apparatus illustrated in FIGS. 9 and 10, the torque is transmitted from the inner chordal surfaces 81f of the drive member 16 to the anvil 18b. The cross-sectional area ratio is much greater along the length of the chordal surfaces 81g of the anvil than in prior devices, reducing the losses due to reflections created by the transmission of longitudinal stress pulses through the anvil and bit.

In the form of invention shown in FIG. 12, a single segment 700 is secured, as by welding material 701, to the drive member 16, this segment having a flat inner chordal face 702 engaging a companion chordal face 703 on the anvil 180. The cross-sectional area through the anvil along the length of its chordal face is much greater than in prior devices, and, therefore, results in greater drilling efficiency in the air hammer apparatus. However, it is preferred to provide a balanced drive mechanism, such as two, three or four uniform, circumferentially spaced segments 700 engaging companion generally chordal surfaces 702 on the anvil.

We claim:

1. In percussion drilling apparatus: a housing structure connectible to a drill string; an anvil in the housing structure; a piston reciprocable in said housing structure for intermittently impacting against said anvil; means for transmitting rotary motion from said housing structure to said anvil comprising one or'more generally chordal surfaces on said anvil, and torque transmitting means on said housing structure in driving surface engagement with said one or more generally chordal surfaces; said generally chordal surfaces being uniformly spaced from each other circumferentially of said anvil; said torque transmitting means comprising metallic segments on said housing structure uniformly spaced from each other circumferentially of said housing structure, said segments having generally chordal surfaces conforming to and in full surface engagement with said generally chordal surfaces on said anvil.

2. In apparatus as defined in claim 1; said anvil being shiftable longitudinally in said housing structure with the generally chordal surfaces on said anvil slidable along the generally chordal'surfaces on said segments.

3. In apparatus as defined in claim 1; saidmetallic segments being removably mounted on said housing structure, and means on said housing structure retaining said segments on said housing structure.

4. In apparatus as defined in claim 1; said generally chordal surfaces being on said segments and anvil planar. I H

v5. In apparatusas defined in claim 1; said one or more generally chordal surfaces on said anvil being concave; said one or more generally chordal surfaces on said segments being convex.

6. In percussion drilling apparatus: a housing structure connectible to a drill string and including a lower terminal drive member detachably secured to a housing section thereabove; an anvil bit shiftable axially in said housing structure; a piston reciprocable in said housing structure for intermittently impacting upon the upper portion of said anvil bit; said anvil bit having a plurality of circumferentially spaced external generally chordal and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces.

8. ln apparatus as defined in claim 6; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto.

9. In apparatus as defined in claim 6; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto; seal means between said anvil bit and drive member to prevent fluid leakage therebetween when the lower end of said drive member engages said anvil bit; and means providing a fluid by-pass between said anvil bit and drive member upon elevation of said drive member with respect to said anvil bit.

10. In apparatus as defined in claim 6; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex.

11. In apparatus as defined in claim 6; said external and inner generally chordal surfaces being planar.

12. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex.

13. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto.

14. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces onsaid anvil bit being concave; said generally chordal surfaces on said segments being convex; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto; seal means between said anvil bit and drive member to prevent fluid leakage therebetween when the lower end of said drive member engages said anvil bit; and means providing a fluid by-pass between said anvil bit and drive member upon elevation of said drive member with respect to said anvil bit. l l

(5/09.) v" r "w an r1 m w! CLLUQLMQAML Or MOBLMLQHON mien-L- 3,804,181 Dated April 16, 1974 Alfred R. Curingon at a].

. IINLIA'LUAT (1;)

it is certified that en's"; appears in the abovc-identifivd patent corrected shown below:

and that said Letters Patent are hereby Column 2,; l in 39 change +b";to -1*ba (301m 6", liri-SG: change "dear" to --'-Nea:-;--.

4 line 65@ change 7290 Fi 1;)? to "200 (Fi 1a)- Column 10, lin'e 5'4: aiipzzel- "being". i I

' ling 54:- aftc er "am r11" insrt "being". Q I

A Signed and sealed this 22nd day of Octobejr .1974;

Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer I j Qommissioner of Patem zs 

1. In percussion drilling apparatus: a housing structure connectible to a drill string; an anvil in the housing structure; a piston reciprocable in said housing structure for intermittently impacting against said anvil; means for transmitting rotary motion from said housing structure to said anvil comprising one or more generally chordal surfaces on said anvil, and torque transmitting means on said housing structure in driving surface engagement with said one or more generally chordal surfaces; said generally chordal surfaces being uniformly spaced from each other circumferentially of said anvil; said torque transmitting means comprising metallic segments on said housing structure uniformly spaced from each other circumferentially of said housing structure, said segments having generally chordal surfaces conforming to and in full surface engagement with said generally chordal surfaces on said anvil.
 2. In apparatus as defined in claim 1; said anvil being shiftable longitudinally in said housing structure with the generally chordal surfaces on said anvil slidable along the generally chordal surfaces on said segments.
 3. In apparatus as defined in claim 1; said metallic segments being removably mounted on said housing structure, and means on said housing structure retaining said Segments on said housing structure.
 4. In apparatus as defined in claim 1; said generally chordal surfaces being on said segments and anvil planar.
 5. In apparatus as defined in claim 1; said one or more generally chordal surfaces on said anvil being concave; said one or more generally chordal surfaces on said segments being convex.
 6. In percussion drilling apparatus: a housing structure connectible to a drill string and including a lower terminal drive member detachably secured to a housing section thereabove; an anvil bit shiftable axially in said housing structure; a piston reciprocable in said housing structure for intermittently impacting upon the upper portion of said anvil bit; said anvil bit having a plurality of circumferentially spaced external generally chordal surfaces; said drive member having circumferentially spaced openings extending therethrough; and segments in said openings having inner generally chordal surfaces conforming to and in surface engagement with said external surfaces, said drive member engaging said segments, whereby torque is transmitted from said drive member through said segments and said inner and external surfaces to said anvil bit.
 7. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces.
 8. In apparatus as defined in claim 6; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto.
 9. In apparatus as defined in claim 6; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto; seal means between said anvil bit and drive member to prevent fluid leakage therebetween when the lower end of said drive member engages said anvil bit; and means providing a fluid by-pass between said anvil bit and drive member upon elevation of said drive member with respect to said anvil bit.
 10. In apparatus as defined in claim 6; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex.
 11. In apparatus as defined in claim 6; said external and inner generally chordal surfaces being planar.
 12. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex.
 13. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto.
 14. In apparatus as defined in claim 6; said housing section surrounding said drive member and segments and engaging said segments to retain said segments in said openings with said inner surfaces engaged with said external surfaces; said generally chordal surfaces on said anvil bit being concave; said generally chordal surfaces on said segments being convex; the lower end of said drive member engaging said anvil bit to transmit drilling weight thereto; seal means between said anvil bit and drive member to prevent fluid leakage therebetween when the lower end of said drive member engages said anvil bit; and means providing a fluid by-pass between said anvil bit and drive member upon elevation of said drive member with respect to said anvil bit. 